Of course, if you own Red Orchestra already you can download the Darkest Hour mod for free via Steam. According to the official description posted by Tripwire, the mod features parachute drops and more recent tanks, plus a brand new gameplay to Red Orchestra:
We will have extra weapons to choose from (more than 20 of them!), we will be able to go “tank hunting” with the American Bazooka, the PIAT or the German Panzerschreck and we’ll be able to experience the new features like bullet suppression and supersonic cracks, while having the option to call in artillery strikes. 12 new vehicles, 11 new maps and lots of new hours of Red Orchestra fun are also delivered for free to the game’s owners, so we can say that it’s a really pleasant and welcomed surprise – Darkest Hour is actually a great addition during these tough times!